(1) Field of the Invention
This invention relates to an apparatus for sealing the skirt of recovery systems which collects the valuable gas from an oxygen blowing converter.
(2) Description of the Prior Art
Oxygen blowing converters generate large quantities of waste gases rich in CO content during the refining of metals by pure oxygen blowing. It is well known to collect such waste gases in the unburnt state at the exit from an oxygen blowing converter to use the CO gas contained in them for valuable purposes. This is normally done by a waste gas recovery apparatus.
A typical recovery apparatus is illustrated schematically in FIG. 3, which is connected to a converter 1 for steel production to draw the waste gases therefrom. A lance 11 is provided for blowing pure oxygen onto the bath of molten pig iron within the converter 1. As is well known, the operation of a converter comprises the three process steps of charging, blowing and discharging. In the blowing step, pure oxygen is blown through an oxygen lance or jet into molten metal in the converter to accomplish refining. The oxygen thus blown and carbon contained within the molten metal react to form a large quantity of waste gas composed principally of CO. The recovery apparatus includes a fan 7 which is run to create a draught that draws by suction the waste gases from the converter 1 into a gas cooler 4.
Dust collectors 5 and 6 are provided to remove the dust contained in the gases before they are conduced to a gas holder 10.
A divergent duct branches off from the main duct at a junction point and is connected at its opposite end to a stack 8. A damper 9 is provided immediately downstream of the junction, in both the main duct and the divergent duct, respectively. When the waste gases are not rich enough in CO content for efficient recovery, as in the initial and final stages of blowing, these dampers 9 are manipulated in such a manner as to guide the waste gases to flow into the divergent duct. The deflected gases are then discharged into the atmosphere through the stack 8, after having being burned at the top portion thereof for complete combustion.
A recovery apparatus is required to be constructed to be a completely airtight structure, mainly for the following two reasons. First, since the waste gases from a converter have a more or less high content of CO, an escape of the waste gas exposes an operator to the possible danger of intoxication, when the operator is in the vicinity of the apparatus. Secondly, admission of atmospheric air into the system can result in a reduction of quantity of the recovered waste gas. In normal practice, to provide a proper seal, a skirt 2 is mounted to enclose about the waste gas outlet where the converter 1 is connected to the gas cooler 4 of the recovery system, at which leak and entrance of atmospheric air are most likely to occur.
Normally, means is provided to move the skirt 2 vertically between a lower position where it closes the waste gas outlet of the converter 1 for waste gas recovery and an upper position where it is held clear out of the way to permit the converter to shift to a tilted position for charging or discharging.
Since the mouth of oxygen blowing converters are rugged on the surface, mainly because of adhered metal and slag accumulated from long operations, the skirt 2 cannot be mounted to enclose the periphery of the converter mouth close enough to provide a physically airtight seal.
Consequently, most of the conventional skirts 2, as illustrated in FIG. 4, are installed at a point some way off from the periphery of the converter mouth 12, with an annular sealing band 11a provided at the lower rim portion of the skirt 2 to give sealing along the external periphery of the converter mouth 12.
However, these converter mouths 12 tend to become irregular on the surface, because of spilt or overflown metal or slag or heat-affected deformations, causing a gap between the sealing band 11a and converter mouth 12.
An improved sealing band was proposed, which is divided into multiple segments of a bandage, each pivotally disposed on a horizontal pivot so that the individual segments can land on the converter mouth 12 at a different angle of tilt thereby closing the rugged mouth surface.
This improved sealing band, however, has been found to pose a serious problem. While efficient to provide proper sealing along the periphery of the converter mouth 12, it causes a gap between the adjacent segments tilted at different angles along their opposite edges.
A further development is shown in FIG. 5, which comprises a double sealing device mounted to enclose about the mouth 13 of the converter 1. A primary sealing assembly consists of an upper annular skirt 2 and a matching intermediate skirt 2' which is brought into contact with the mouth 13. An annular secondary sealing band 15 is provided to encircle the mouth 13 external of the primary sealing assembly. An annular bellows 16 is provided to interconnect the upper and intermediate skirts 2 and 2'. The annular secondary sealing device 15 is connected to the primary sealing assembly by another annular bellows 17.
A hydraulic cylinder 18 is fixedly mounted on the upper annular skirt 2 and has its reciprocable piston secured to the annular secondary sealing device 15. The hydraulic cylinder 18 is actuated to lift up the entire skirt assembly with its primary and secondary sealing means by means of the piston, when the converter 1 has to be tilted for charging or discharging. During the gas recovery operation, on the other hand, the hydraulic cylinder 18 is released to hold the sealing devices 2' and 15 in close contact with the mouths 13 and 14.
A similar skirt sealing device of double structure is illustrated in FIG. 6, which also employs a pair of annular bellows 19 and 20. An intermediate water-cooled annular wall 21 is provided to stand between a portion of skirt 2 comprised of the lower flared end of the skirt which encloses the converter mouth 24 and sealing device 22. This wall 21 is properly cooled enough to allow an overflow of molten slag that might come down the converter mouth 24 to cool to solidification, in order to keep smooth in that outer area of the flanged mouth 24 where the sealing device 22 is held in sealing contact with the mouth surface.
In the last mentioned two conventional devices, although the bellows are employed to insure both sealing and efficient vertical movement of the double sealing device, their frequent use is found to pose serious problems.
For example, dust tends to deposit in the bottoms of the folds in the bellows, with a resultant reduction in the flexing of the bellows. In addition, ideal application requires a bellows to be as thin as possible. However, a bellows made of thin material, exposed to the extremely high temperature environment of steel refining and repeated extension and contraction, tends to degradate in short periods of service life.